The present invention generally relates to the field of military ordinance. In particular, it relates to a new sabot design for use in Kinetic Energy (KE) projectiles, which reduces the parasitic weight of the sabot upon launch and transforms the parasitic weight into propulsion gases that provide a greater velocity to the projectile.
Kinetic Energy (KE) projectiles are well known in the ammunition community and are made in small, medium and large caliber from 20 to 120 mm. FIGS. 1 and 2 illustrate cross sectional views of KE projectiles 10 and 205 with two types of sabots 15 and 210. The standard sabot 15 (also referenced as pusher sabot 15) is illustrated in FIG. 1, and the puller sabot 210 is illustrated in FIG. 2. Both the standard sabot 15 and pusher sabot 210 are well known in the ammunition community.
Sabots are attached to the projectile rod by threads or buttress grooves. The function of a sabot is to fill the space between the gun tube and the projectile rod and, along with the obturator (i.e., a plastic ring that attaches to the back of the sabot), prevent propellant gases from blowing past the projectile. The sabots also support the rod during gun launch as it travels up the gun tube. The sabots are usually made of three pieces or petals that are discarded from the rod as soon as the projectile exits the gun tube and gets past the gun gases.
A retaining ring (not shown) is imbedded in the front and back of the sabot. This retaining ring holds the petals of the sabot together.
When the projectile is launched from the gun tube, the scoop in front of the sabot captures the air and therefore a force is exerted on the sabots. When the force exceeds the strength of the retaining rings, the retaining ring breaks allowing the petals of the sabot to come apart and move away from the projectile rod. After the sabot is discarded, the projectile rod, nose and fin travel to the target (the projectile rod, nose and fin are known as the in-flight projectile and when the sabots are attached the projectile is known as the in-bore projectile). The target is usually protected with heavy armor. The projectile rod penetrates the target utilizing the very high velocity (kinetic energy) at which the rod is traveling. An increase in projectile rod velocity increases the armor thickness that the rod can penetrate.
Currently, the standard sabot used in ammunition is considered “parasitic weight”. The sabot's sole function is to act as a carrier of the penetrator during launch. The sabot mates with the penetrator and provides a pushing surface for gun gasses to push the projectile out of the gun tube. The projectile exits with a specific muzzle velocity, and flies towards its target. Generally speaking, the greater the penetration, the more lethal the projectile, and the greater the muzzle velocity of the projectile, the greater the penetration. The sabot is necessary because it ensures that the greatest possible force is applied to the penetrator by the gases caused during the propellant ignition phase of the interior ballistic event. However, after the projectile leaves the gun tube, the sabot is discarded, allowing the penetrator to fly freely towards its target.
The in-bore projectile is part of a cartridge assembly (not shown) that holds the projectile to allow chambering into the gun tube and also contains the propellant and primer. When the soldier wants to fire the projectile, an electrical signal is sent that ignites the primer. The flame spread from the primer sets off the propellant that creates high-pressure gases. When the force of the gases exceeds the force to push the projectile and obturator, the projectile begins to move at a very high velocity.
The sabots are typically made of very strong materials such as aluminum (7076 T6) or ultem composites reinforced with carbon fiber. Sabots are subject to very high shock loads known as setback or g forces when the projectile is launched in the gun. They are therefore designed to meet these forces without breaking when fired from a gun. Setback forces can be as high as 70,000 g”s for some KE projectiles. Gun pressures can be as large as 103,000 psi for large caliber systems.
At shot start, which term is used to reference when the projectile begins to move, the projectile sees an increase in gravitational (or G−) forces, G”s, and pressures as it travels down the gun tube until the maximum G and maximum base pressure on the projectile is reached. This takes place usually within the first ⅓ of the length of the gun tube.
Then, as the projectile travels up the remainder of the gun tube, the pressures and forces on the projectile decrease rapidly to a fraction of their maximum value. The problem of parasitic weight comes into play between the moments when the peak force and pressure is reached inside the tube and when the projectile exits the gun tube. The sabot is structurally designed to withstand the maximum force and pressure reached inside the gun tube. However, after the maximum pressure is reached the pressure decreases, and the extra mass of the sabot needed to with-stand the peak values becomes superfluous.
Not only does this extra mass become unnecessary, it becomes a hindrance in that it limits the acceleration of the projectile in the tube. While the extra mass is needed to withstand the maximum force and pressure values, some of this mass becomes almost completely parasitic as the forces and pressures decrease. Since the sabot is typically between 25–30% of the total projectile mass, considerable energy is wasted during launch. It has been estimated that up to 2 lbs of the sabot is not needed after peak pressures and G forces are achieved.
What is therefore needed is a method to reduce the parasitic weight of the projectile without compromising its structural integrity. The need for such a system has heretofore remained unsatisfied.